1. Field of the Invention
The present invention relates to an electron source and an electron beam apparatus using the electron source.
2. Related Background Art
Generally, an image-forming apparatus utilizing electrons requires an enclosure for maintaining a vacuum atmosphere therein, an electron source for emitting electrons and a drive circuit for the electron source, an image-forming member such as a fluorescent substance which emits light upon impingement of electrons thereon, and an accelerating electrode and a high-voltage power supply for accelerating electrons toward the image-forming member. Some of image-forming apparatus using flat enclosures, such as thin-type image display devices, employs support posts (spacers) to provide a structure endurable against the atmospheric pressure.
In such an image-forming apparatus, when electrons are accelerated to fly in the enclosure, residual gas, etc. residing in the vacuum atmosphere and on the fluorescent substance are ionized and created positive ions are accelerated by the accelerating electrode to fly toward the electron source. If the positive ions impinge upon the electron source, particularly an electron-emitting device having an electron-emitting region, the electron source is deteriorated. Therefore, to prevent charged particles from directly impinging upon the electron-emitting device is important in achieving longer service life and higher reliability of the electron source.
As one expedient for preventing deterioration of the electron source due to the phenomenon described above, U.S. Pat. No. 4,155,028 discloses an electrostatic deflecting system. FIG. 27 shows a schematic construction of the disclosed system. Denoted by 3011 is an electron-emitting device comprising a hot cathode, 3012 is a first grid, 3013 is a second grid, and 3014 is an accelerating electrode. The first and second grids 3012, 3013 are arranged to extend at a certain angle defined therebetween, and are supplied with the same potential that is sufficient to draw electrons out of the electron-emitting device, but insufficient to create positive ions. Solid lines 3015 in FIG. 27 represent respective paths of electrons emitted from the electron-emitting device 3011. The electron paths are deflected near the second grid 3013 to advance toward the accelerating electrode 3014 perpendicularly. On the other hand, positive ions produced by the accelerating electrode 3014 have larger mass than electrons and hence are less deflected near the second grid 3013 to follow paths indicated by dotted lines 3016. Accordingly, the positive ions will not directly approach the electron-emitting device 3011. Thus, in U.S. Pat. No. 4,155,028, deterioration of the electron-emitting device is prevented by using a plurality of control electrodes which are arranged obliquely with respect to the electron-emitting device.
As electron-emitting devices for use in an electron source of an image-forming apparatus, there are also known cold cathode devices in addition to hot cathode devices as described above. Cold cathode devices include electron-emitting devices of field emission type (hereinafter abbreviated to FE), metal/insulating layer/metal type (hereinafter abbreviated to MIM), surface conduction type, etc.
Examples of FE electron-emitting devices are described in, e.g., W. P. Dyke 8 W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical Properties of Thin-film Field Emission Cathodes with Molybdenum Cones", J. Appl. Phys., 47, 5248 (1976).
One example of MIM electron-emitting devices is described in, for example, C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32, 646 (1961).
One example of surface conduction electron-emitting devices is described in, e.g., M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965).
A surface conduction electron-emitting device utilizes a phenomenon that when a thin film having a small area is formed on a substrate and a current is supplied to flow parallel to the film surface, electrons are emitted from the film. As to such a surface conduction electron-emitting device, there have been reported, for example, one using a thin film of SnO.sub.2 by Elinson cited above, one using an Au thin film [G. Dittmer: "Thin Solid Films", 9, 317 (1972)], one using a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)], and one using a carbon thin film [Hisashi Araki et. al.: "Vacuum", Vol. 26, No. 1, 22 (1983)].
As a typical configuration of those surface conduction electron-emitting devices, FIG. 28 shows the device configuration reported by M. Hartwell in the above-cited paper. In FIG. 28, denoted by reference numeral 3101 is an insulating substrate. 3102 is a thin film for forming an electron-emitting region which comprises, e.g., a metal oxide electroconductive thin film formed by sputtering into an H-shaped pattern. An electron-emitting region 3103 is formed by the energizing process called forming (described later).
In those surface conduction electron-emitting devices, it has heretofore been customary that, before starting emission of electrons, the electron-emitting region forming thin film 3102 is subjected to the energizing process called forming to form the electron-emitting region 3103. The term "forming" means a process of applying a voltage across the electron-emitting region forming thin film 3102 to locally destroy, deform or denature it to thereby form the electron-emitting region 3103 which has been transformed into an electrically high-resistance state. The electron-emitting region 3103 comprises a crack or the like formed in a portion of the electron-emitting region forming thin film 3102, and electrons are emitted from the vicinity of the crack. The electron-emitting region forming thin film 3102 including the electron-emitting region which has been formed by the forming process will be hereinafter referred to as an electron-emitting region including thin film 3104. In the surface conduction electron-emitting device after the forming process, a voltage is applied to the electron-emitting region including thin film 3104 to supply the device with a current, whereupon electrons are emitted from the electron-emitting region 3103.
As an example in which a number of surface conduction electron-emitting devices are formed into an array, there is an electron source wherein surface conduction electron-emitting devices are arranged side by side, both ends of the devices are interconnected by respective wirings in parallel to form one row of an array, and a number of rows are arranged to form the array (see, e.g., Japanese Patent Application Laid-open No. 64-31332 in the name of the same assignee).
Meanwhile, various image-forming apparatuses are constructed by combining an electron source which has an array of numerous surface conduction electron-emitting devices, with a fluorescent substance as an image-forming member which radiates visible light upon impingement of electrons emitted from the electron source (see, e.g., U.S. Pat No. 5,066,883 issued to the same assignee). This type of image-forming apparatus is expected to become popular and take the place of CRTs, because it is self-luminous (i.e., emission type), is relatively easy to manufacture with a large screen size, and has good display quality.
In an image-forming apparatus disclosed in Japanese Patent Application Laid-open No. 2-257551 in the name of the same assignee, for example, desired ones of surface conduction electron-emitting devices formed in a large number are selected by applying appropriate drive signals to wirings (i.e., row-directional wirings) each interconnecting the surface conduction electron-emitting devices in parallel which are arranged side by side, and to control electrodes (called grids) which are disposed in a space between an electron source and a fluorescent substance to extend in a direction (i.e., column-direction) perpendicular to the row-directional wirings.